The present invention relates to photographic equipment, and more particularly to a camera permitting development of films by diffusion-transfer process within the camera.
It is known to provide a type of camera in which a film be processed as well being exposed, whereby it is possible to obtain a positive print of an object to be photographed, almost immediately after a film in the camera has been exposed to image rays from the object. Film employed in such a camera is a special type, each unit of which comprises a combination of a negative film portion and a positive film portion associated with a sac containing a solution of photographic processing chemicals. This type of camera goes under a variety of popular or trade names, such as auto-copy, or auto-process camera. Similarly, film associated with this type of camera goes under a variety of appellations, for example, instant-print film, film-sheet, or monosheet. For the purposes of the present description, this type of camera, and the type of film associated therewith, will be referred to, respectively, as auto-process camera and monosheet.
Monosheets are normally provided in a cassette, or pack, which holds a definite number of monosheets, and which is loadable into an auto-process camera. Each cassette comprises a suitable light-proof cover, which protects the set of monosheets in the cassette from exposure to light, prior to use of the monosheets, and which, when the cassette has been loaded into an auto-process camera, is removable by a suitable means provided in the camera. For each photograph taken, the negative film portion of a monosheet is exposed, and te monosheet is then withdrawn from the cassette, or pack, by means provided in the auto-process camera, passed through processing rolls, or similar means, which extrude the processing solution from the sac portion of the monosheet, thereby effecting diffusion and transfer of the image of the object photographed onto the positive film portion of the monosheet, after which the monosheet is moved through a suitable opening to the exterior of the camera. A photographer is thus saved the trouble of having to go to a separate establishment in order to obtained a completed copy, and also, since processing is extremely rapid, may know almost immediately whether or not a photograph has been taken in a required manner, and so whether or not it is necessary to take another shot. Various advances have been made relative to monosheets, for example by the provision of monosheets having improved qualities, or different speeds, or sensitivities to light. There has also been progress relating to auto-process cameras, but one outstanding drawback of conventional auto-process cameras is that the cameras do not permit unloading and subsequent reloading of one and the same cassette containing monosheets. That is, once a particular cassette has been loaded into a conventional auto-process camera, and the light-proof cover thereof has been removed, if the cassette is unloaded while there are still unexposed monosheets remaining therein, the foremost remnant monosheet is completely exposed, through an unprotected main front opening of the cassette, and other remnant monosheets are at least partially exposed by light entering the cassette via monosheet extraction slits or similar portions. Because of this, if, after initially loading a conventional auto-process camera with a cassette containing monosheets having a certain sensitivity, and after taking a certain number of shots, a photographer wishes to photograph a scene or object requiring monosheets having a different sensitivity, or other characteristics, he or she must either waste the remaining monosheets, by loading a new cassette, or renounce taking the required shots. A photographer is faced with a similar problem when there are only 2 - 3 unexposed monosheets left in a cassette loaded in a camera, and he or she anticipates taking 6 - 8 shots in rapid succession, for example, of an action scene, such as a race. In this case also, the photographer must either reload a new, full cassette, and so waste the remaining 2 - 3 monosheets, or renounce taking the required number of shots.